The present invention relates to an embroidery sewing machine. More specifically the invention relates to a lockstitch embroidery sewing machine wherein a piece of needle thread and a piece of lockstitch bobbin thread join in the formation of lockstitch seams while a cord supplied from the other source is wound with turns of winding thread supplied from a bobbin which is in turn locked by the piece of needle thread during the process of stitch formation.
In a conventional embroidery sewing machine, a rotatable rotary ring equipped with a drive gear on the upper periphery thereof is arranged on a cylinder. A protruding support arm having an extending shaft for mounting a bobbin on which a winding thread is wound is secured fixedly on the periphery of the rotary ring. The shaft for mounting the bobbin thereon is designed to be tilted or slanted outwardly and downwardly with respect to an axis of a needle bar.
While a lockstitch seam is formed by means of a needle thread and a lockstitch bobbin thread, as is well-known to those skilled in the art, the drive gear of the rotary ring is driven by a driving mechanism of a prior art to rotate the rotary ring around the cylinder accompanied by the bobbin mounted on the support arm.
While the bobbin rotates around the cylinder, a piece of winding thread is unwound therefrom while a piece of cord supplied from other source is wound with turns of the piece of winding thread which in turn is locked by the piece of needle thread to form lockstitch embroidery seams.
However, the structure of the rotary ring rotatable arranged around the cylinder brings forth an increase of orbital radius of the rotation when the bobbin mounted on the tilted or slanted shaft of protruding support arm is rotated around the cylinder together with the rotary ring.
Therefore, an operator should always keep away from the rotation radius of the support arm to avoid bumping thereagainst, whereby an effective operation of the machine is hindered. There are also other drawbacks such as untimely and inadvertent unwinding of winding thread from the bobbin when the rotation of rotary ring comes a sudden stop while the bobbin still tends to continue to unwind the thread therefrom due to inertia created by the rotation thereof.
Accordingly, it is an object of this invention to provide a new bobbin and cylinder structure designed for overcoming heretofore mentioned drawbacks.
To replace an embroidery fabrics positioned underneath a cylinder nipple it is necessary to lift the cylinder upward and to keep it at a predetermined raised position in order to keep ample space or room for the replacement of embroidery fabrics. In a conventional embroidery sewing machine, the lifting of the cylinder is usually operated manually.
It is another object of the invention to provide a new lifting device for cylinder which is mechanically operated.